The system and method disclosed herein relates to printing systems that generate images onto continuous web substrates. In particular, the disclosed embodiment relates to duplex registration of side 1 and side 2 images.
Printers provide fast, reliable, and automatic reproduction of images. The word “printer” as used herein encompasses any apparatus, such as a digital copier, book marking machine, facsimile machine, multi-function machine, etc., which performs a print outputting function for any purpose. Printing features that may be implemented in printers include the ability to do either full color or black and white printing, and printing onto one (simplex) or both sides of the image substrate (duplex).
Some printers, especially those designed for very high speed or high volume printing, produce images on a continuous web print substrate. In these printers, the image substrate material is typically supplied from large, heavy rolls of paper upon which an image is printed instead of feeding pre-cut sheets from a bin. The paper mill rolls can typically be provided at a lower cost per printed page than pre-cut sheets. Each such roll provides a very large (very long) supply of paper printing substrate in a defined width. Fan-fold or computer form web substrates may be used in some printers having feeders that engage sprocket holes in the edges of the substrate.
Typically, with web roll feeding, the web is fed off the roll past one or more print head assemblies that eject ink onto the web, and then through one or more stations that fix the image to the web. A print head is a structure including a set of ejectors arranged in at least one linear array of ejectors, for placing marks on media according to digital data applied thereto. Print heads may be used with different kinds of ink-jet technologies, such as liquid ink jet, phase-change ink, systems that eject solid particles onto the media, etc.
Thereafter, the web may be cut in a chopper and/or slitter to form copy sheets. Alternatively, the printed web output can be rewound onto an output roll (uncut) for further processing offline. In addition to cost advantages, web printers can also have advantages in feeding reliability, i.e., lower misfeed and jam rates within the printer as compared to high speed feeding of precut sheets through a printing apparatus.
A further advantage is that web feeding from large rolls requires less downtime for paper loading. For example, a system printing onto web paper supplied from a 5 foot diameter supply roll is typically able to print continuously for an entire shift without requiring any operator action. Printers using sheets may require an operator to re-load cut sheet feeders 2 to 3 times per hour. Continuous web printing also provides greater productivity for the same printer processing speed and corresponding paper or process path velocity through the printer, since web printing does not require pitch space skips between images as is required between each sheet for cut sheet printing.
A requirement of continuous feed duplex printing is registration of the side 1 image to the side 2 image. A standard technique to perform this registration is to sense registration marks on preprinted forms. A sensor detects these marks and uses the timing to maintain a fixed spacing between the registration mark and the printed page. A solid ink direct marking continuous feed printer presents a unique situation and the standard approach may not work because the paper is heated in the print zone which causes lateral size paper shrinkage between side 1 and side 2. A single registration mark cannot monitor the magnitude of paper shrinkage throughout the duplex paper path which is required for registration across all colors. The long print zone can give rise to drift of the paper in the lateral direction so cross process side 1 to side 2 registration must also be maintained.
Accordingly, in answer to the above-mentioned problem, a system and method is disclosed for achieving registering of side 1 and side 2 images by sensing marks on both sides of a web with a single IOWA sensor and relying on light transmission through paper. The side not facing the IOWA sensor utilizes increased contrast (black toner), mark width, and repeats to increase the detectability of the back side test target. The registration of the marks on both sides of the sheet are compared with respect to each other and adjustments to some combination of position, timing, and image magnification are made.
Various of the above-mentioned and further features and advantages will be apparent to those skilled in the art from the specific apparatus and its operation or methods described in the example(s) below, and the claims. Thus, they will be better understood from this description of these specific embodiment(s), including the drawing figures (which are approximately to scale) wherein:
With initial reference to
The process path 130, which is the actual path along which the media 126 proceeds, includes process path segment 132 which is located adjacent to the print stations 102 and 104, and process path segment 134 which is located adjacent to the print stations 106 and 108. The process path segment 132 is defined by rollers 140 and 142 while the process path segment 134 is defined by rollers 144 and 146. A roller 148 defines a horizontal turn in the process path. Alignment of the print stations 102, 104, 106, and 108 with the respective process path segment 132 or 134 is controlled by an alignment control system such as disclosed in U.S. patent application Ser. No. 12/175,879, filed Jul. 18, 2008, by Howard A. Mizes et al, and entitled CONTINUOUS WEB PRINTING SYSTEM ALIGNMENT METHOD and U.S. patent application Ser. No. 12/372,294, filed Feb. 17, 2009, by Howard A. Mizes et al, and entitled SYSTEM AND METHOD FOR CROSS-PROCESS CONTROL OF CONTINUOUS WEB PRINTING SYSTEM, both of which are included herein by reference to the extent necessary to practice the present disclosure.
In order to accomplish duplexing on continuous web 126, the web is directed into an inverter mechanism 300 which turns the web over for printing on the opposite side of side 2. Inverter mechanism 300 turns web 126 over as shown in
With further reference to
The process path 230, which is the actual path along which the media 126 proceeds, includes process path segment 232 which is located adjacent to the print stations 202 and 204, and process path segment 234 which is located adjacent to the print stations 206 and 208. The process path segment 232 is defined by rollers 240 and 242 while the process path segment 234 is defined by rollers 244 and 246. A roller 248 directs the web 126 under an image on web array sensor (IOWA) 138 that is held steady by a backer roll 139. The IOWA sensor 138 is a full width image contact sensor, which monitors the ink on the web 126 as the web passes under the IOWA sensor. When there is ink on the web 126, the light reflection off of the web 126 is low and when there is no ink on the web 126, the amount of reflected light is high. When a pattern of ink is printed by one or more of the heretofore-mentioned print heads, the IOWA sensor 138 may be used to sense the printed mark and provide a sensor output to a control device, such as, a computer for processing. The paper passes through another series of rolls and stations that condition the image before it is taken up by a rewinder or processed by other finishing equipment.
Ink jet printing systems as described above consist of a series of individual print heads jetting ink of different colors and located at different positions along the print path. If these heads are not perfectly aligned in the lateral position there may be gaps or overlap at the transitions between the last jet on one print head and the first jet on the adjacent print head. If the timing of firing the jets is not coordinated with the web velocity and the spacing between the print heads along the print path, there will be a process direction misregistration between colors or at the transition between print heads.
Heretofore, simplex registration has been maintained by printing a test pattern of dashes from individual heads. The dashes are imaged with the IOWA sensor and the lateral and process direction position of each dash is calculated from the image. Because the nozzle which produces each dash is known, the position of every print head can be inferred from the test pattern. The measured locations of the heads are compared to the desired location of the heads. The heads are physically moved by motors in the lateral direction and the timing of the firing in the process direction. In this way registration is maintained.
In answer to this problem and in accordance with the present disclosure, an improved method and apparatus is disclosed that includes a modification of the registration pattern that is easily detected using a show through image. The show through image will be very faint, so there are three changes in the test pattern that can be used to increase the signal: (1) increased contrast because registration for each side is maintained separately, only one of the print heads in series is needed to determine the side 1 or side 2 registration. The high contrast black print head can be chosen for the show through test pattern; (2) increased width because a single pixel wide dash will give a weak show through signal, neighboring nozzles can be used to create a wider dash; and (3) a repeated signal because since the show through is weak, it can be difficult to distinguish a show through signal from variations in the reflectance of the web material. This problem is exacerbated from thick stock. However, if the dash pattern is repeated as in a ladder chart, the periodic pattern will be more easily detected in spite of the paper structure.
The IOWA backer roll 139 is typically white or a highly reflective surface. This requirement makes the IOWA signal insensitive to natural variations in the paper thickness due the structure of the paper fibers. This insensitivity is required for the IOWA sensor to robustly detect missing jets and to adjust print head uniformity. The white backer roll 139 also meets the requirements for side 1 or side 2 detection. When black ink is imaged on the other side of the paper, it prevents light that transmits through the paper to be reflected by the backer roll and is thus the source of the show through signal.
It should be understood that variations of this pattern that are more robust against larger misregistrations or can measure changes in registration across the lateral direction can also be used.
The print job then begins in block 412. At regular intervals, as shown in block 414, a side 1 interdocument zone (IDZ) duplex registration pattern is printed in the cutting zone between two images when the paper passes through the first marking engine or takes its first pass through the marking engine in Mobius configuration. In block 416, when this IDZ arrives in the next marking engine or in its second pass through the marking engine in Mobius configuration, the side 2 IDZ duplex registration pattern is printed on side 2. The IDZ duplex registration pattern is then captured in block 418 when it arrives at the IOWA sensor 138. The image is processed and the measured spacing between the side 1 dashes and the side 2 dashes is determined in block 420. If the spacing is different, then in block 422 the head delays are adjusted, the heads are moved, and the image magnification is changed.
Tests have shown that the show through signal is strong enough to measure the side 1 and side 2 registration to the accuracy required as depicted in a section of a captured image in
The side 2 ladder chart, which is facing the sensor, is clearly resolved. However, the side 1 dashes from the first pass through the sensor is also seen in the test pattern. The contrast however is much lower and in some locations it is difficult to resolve the individual dashes.
To test the ability of the image processing algorithms to accurately measure the side 1 to side 2 registration, this image was printed multiple times throughout a long job. The image was printed on 75 gsm stock. The registration between side 1 and side 2 was intentionally not maintained in order to produce a variation in side 1 to side 2 registration, as shown in
The process direction position of the side 1 and side 2 ladder chart was determined by measuring the amplitude of a signal at the known period of the ladder chart for each scanline in the image. This signal is large over a side 2 ladder chart, moderate over the show through of the side 1 ladder chart, and small over a blank section of paper. A plot of the amplitude of this signal as a function of scanline is shown in
The variation in the process direction position was measured by detecting the edges of adjacent tics of
To calculate the lateral alignment, the profile of both the side 1 and side 2 dashes were obtained.
In
It should not be known that a method and apparatus has been disclosed for maintaining side 1 and side 2 registration for duplex continuous web printing that uses a single full width array sensor for side 1 to side 2 registration to sense marks on both sides of the web and relying on light transmission through paper. The side not facing the full width array utilizes increased contrast, mark width and repeats so as to make effective image show through. The image of marks on both sides of the paper are compared with respect to each other and adjustments to some combination of position, timing, and image magnification are made as required. Thus, a cost and space advantage is obtained by eliminating a second side array sensor.
The claims, as originally presented and as they may be amended, encompass variations, alternatives, modifications, improvements, equivalents, and substantial equivalents of the embodiments and teachings disclosed herein, including those that are presently unforeseen or unappreciated, and that, for example, may arise from applicants/patentees and others. Unless specifically recited in a claim, steps or components of claims should not be implied or imported from the specification or any other claims as to any particular order, number, position, size, shape, angle, color, or material.
Number | Name | Date | Kind |
---|---|---|---|
4619278 | Smeed et al. | Oct 1986 | A |
6118950 | Wibbels et al. | Sep 2000 | A |
7216952 | Claramunt et al. | May 2007 | B2 |
7967517 | Wada | Jun 2011 | B2 |
20040136733 | Kretschmann et al. | Jul 2004 | A1 |
20040160468 | Kim et al. | Aug 2004 | A1 |
20050183603 | Trelewicz et al. | Aug 2005 | A1 |
20050276649 | Min | Dec 2005 | A1 |
20060023057 | Jung | Feb 2006 | A1 |
20070175351 | Boness | Aug 2007 | A1 |
20070213215 | Dashiell et al. | Sep 2007 | A1 |
20070222805 | Moscato et al. | Sep 2007 | A1 |
20080278757 | Wong | Nov 2008 | A1 |
20100091334 | Qiao et al. | Apr 2010 | A1 |
20100201774 | Motojima | Aug 2010 | A1 |
20100230527 | Ray | Sep 2010 | A1 |
20100315461 | Mongeon et al. | Dec 2010 | A1 |
Number | Date | Country |
---|---|---|
2001058446 | Mar 2001 | JP |
Entry |
---|
Machine Translation of JP 2001058446 A, JPO, Jan. 21, 2012. |
U.S. Appl. No. 12/175,879, filed Jul. 18, 2008, by Howard A. Mizes et al, and entitled Continuous Web Printing System Alignment Method. |
U.S. Appl. No. 12/372,294, filed Feb. 17, 2009, by Howard A. Mizes et al, and entitled System and Method for Cross-Process Control of Continuous Web Printing System. |
Number | Date | Country | |
---|---|---|---|
20100329756 A1 | Dec 2010 | US |